Abstract: In this study, the data of geo-electric resistivity, geo-electric field, and extremely low frequency(ELF) observation within 400km of the Guye Ms5.1 earthquake on July 12th, 2020, is analyzed using a combination of time-domain waveform analysis, sliding Fourier subtract annual variation analysis, normalized variation rate method(NVRM), and geo-electric azimuthal method. After eliminating the influencing factors such as operation status, observational environment, and the spatially electromagnetic effect, we consider that 6 geo-electric resistivity stations exhibit a variation of “trend decrease--accelerated decrease--postseismic recovery” and 7 stations with a threshold value of the normalized variation rate exceeding±2.4 within one year before the earthquake. In Luan county, the intensity of the geoelectric field in north-south and north-western directions decrease and then rise back prior to the earthquake. In addition, the azimuth shifts to the direction of the Guye earthquake in the preseismic period, and then returns to the direction of the Luan-Leting fault. The ELF stations in Wen’an and Fengning has precisely recorded the coseismic change of the 16Hz natural magnetic field, in which the variation of the vertical component is twice larger than that of the horizontal component. Under the condition of large subsurface structure difference beneath the stations, the observed electric values from the two stations are distinctively different; moreover, the coseismic disturbance is submerged by the background noise. By inversing the data collected from the ELF stations in the capital area, the subsurface electric structure is obtained. The structure indicates that Guye earthquake occurs near the boundary where the electric property changes. Meanwhile, it shows high electric resistivity in northern areas, low electric resistivity in southwestern areas, and partially low electric resisitivity in Baodi and Wen’an. Further, the characteristics of the electromagnetic phenomenon of Guye earthquake are preliminarily analyzed. With regard to the problem of anomalously spatial selectivity, we believe it may be related to the two main conjugated structure directions in the capital area, which lie in NEE and NW, respectively. Finally, the study also enlighten researchers that the investigation of the mechanism of seismic electromagnetic anomaly should be started from the coseismic phenomenon, and then deepened through the aspect of seismic signal source and propagation path.

Key words: Guye Ms5.1 earthquake, georesistivity, geoelectricity field, extremely low frequency(ELF), electromagnetic anomaly

摘要： 使用时间域波形分析、滑动傅式去年变分析、归一化变化速率方法和矢量方位角方法处理分析了2020年7月12日古冶Ms5.1地震400km范围内地电阻率、地电场、极低频观测数据。在排除各台站仪器运行、台站观测环境、空间电磁活动等影响因素后，认为有6个地电阻率台站震前出现了趋势性下降-加速下降-震后恢复的变化过程，7个地电阻率台站在震前一年内归一化变化速率超过±2.4阈值；滦县地电场南北和北西向测道震前三个月出现先下降后回升的变化，且矢量方位角在震前向古冶地震方向偏移，后恢复为沿台站所在滦县-乐亭断裂方向；文安和丰宁极低频台清晰记录到16hz天然源磁场同震变化，磁场垂直分量变化超过水平分量2倍，受台站地下结构巨大差异性影响，两个台站电场观测值差别较大，且电场同震扰动淹没在背景噪声中。本文利用首都圈极低频台站观测数据反演的地下电性结构，古冶地震发生在电性发生变化边界附近，北边高阻区，西南方向为低阻区，宝坻和文安处于局部低阻区，初步分析了古冶地震电磁现象特征。针对异常空间选择性问题，认为可能与京津唐地区NEE和NW向两个主要共轭构造方向有关。对地震电磁异常机理的研究，应该从地震电磁同震现象入手，从地震电磁信号产生的源和传播路径两方面展开。

关键词: 古冶Ms5.1地震, 地电阻率, 地电场, 极低频, 电磁异常